The production of fiber-reinforced hollow rods from graphite fibers conventionally involves the steps of forming the fibers into a sheet-like prepreg, cutting the sheet stock to the appropriate pattern for the ultimate product, wrapping the prepreg around a mandrel (whether or not tapered), curing the epoxy, and removing the mandrel to form the product. Several layers or plies of wrapped prepreg can be used. The number and orientation of the fibers within the plies, both relative to each other and with respect to the longitudinal axis of the mandrel, can be varied to modify characteristics of the rod. Significant investments in time, capital, and training are made in the commercial manufacture of such articles. Such investments are not readily changed or discarded. In the face of such resistance, it is desirable that any improvements in the strength of the manufactured article be performed in a manner that does not significantly change the techniques used to make such conventional hollow rod articles.
The impact strength of hollow rod articles is important, particularly when such rods are used as components in sporting goods where longitudinal impact, flexing, and shear forces (intended or accidental) are experienced. Higher impact strengths increase the useful lifetime of the product and, in some instances, enhance its performance spectrum.
Graphite fibers represented a significant advance in the art both in terms of weight savings, flex, and strength for hollow rods used in sporting goods. Unfortunately, graphite fishing rods still get slammed in car doors, graphite composite golf shafts do still break (usually at the hosel connection), and arrow shafts do snap. It would be desirable to have a way to increase the impact strength of hollow rod articles, such as fishing rods, golf shafts, and arrow shafts made from graphite composites.
Recently, nickel-coated graphite fibers have been become available that exhibit a higher impact strength relative to conventional graphite fibers. Those in the electronics and battery industries have used such fibers as shielding, as electrically conductive members, and as an electrode. The aircraft industry has investigated use of the fibers as structural components for the increased impact strength without significant addition of weight.
Nickel-coated graphite fibers are significantly more expensive than conventional graphite fibers. Prices for the nickel-coated fibers are at least twice that of graphite. It would be desirable to have a way to make use of the higher impact strength of coated graphite fibers for hollow rod products without incurring the significant additional expense of using only the nickel-coated fibers in the composite.